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Meteorites

It was
by chance that I acquired my first meteorite. It was around Christmas
time of 2006 and I was shopping for last-minute stocking stuffer gifts
for my wife and stepkids. Even though I am the only hardcore astronomy
nut in the bunch, the rest of my immediate family has always been
interested in space-related subjects. So when I ran across an online ad
for cheap meteorites, I took notice. These meteorites were hardly
impressive to look at. They were tiny pebbles about the size of a dime,
but they were priced just right at five bucks. At first, I couldn't
believe that one could own a meteorite so cheaply and easily. So using
Google, I did a little homework on meteorites and the seller - to make
sure the offer was legit. I soon discovered that although meteorites
are considered quite rare, they are actually more available than most
people think. The Earth is a large target whipping around the Sun in
space, and it gets struck by meteorites at a constant and steady rate -
like bugs hitting the windshield of a moving car. Most of these
meteorites fall into the oceans which cover the bulk of the Earth's
surface. Many others fall into inhospitable areas were they are
unlikely to be found - jungles, mountaintops, forests, etc. However, a
good number of meteorites land in areas where they are easily
identified and collected - snowfields, deserts, dry lake beds, and
plowed fields. In areas such as those, a strange looking rock tends to
stand out like the proverbial sore thumb, and someone with the right
knowledge can easily spot the meteorite and collect it. Not only do
meteorites fall regularly (and get found regularly), but there are also
dozens of types of meteorites. With being some more rare and
interesting than others. Just like collecting conventional Earth-rocks,
there is a thriving culture of hobbyists who collect and enjoy
meteorites.

Collecting
meteorites is
related to the field of meteoritics (the study of meteorites), and itís
a branch of planetary science that is not only accessible to the
layman,
but
the layman is actually encouraged to participate. While I was waiting
for
my first meteorites to arrive in the mail, I did a lot of reading up on
them
and by the time the mailman finally brought my space rocks, I was
excited
like a kid in anticipation of Christmas morning. When the package
arrived,
I eagerly tore it open and saw a handful of small brown pebbles that
resembled
pieces of dog food. They were heavy for their small size, very smooth,
and
strongly attracted to a magnet due to their inherent metal content. But
the
most fascinating aspect of these unassuming little stones was their
origin.
In my hand, I was holding a rock from outer space that was as old as
the
Earth itself. These meteorites had formed out of the solar nebula
around
the same time that the planets had formed - over 4.5 billion years ago.
Long
before the first single-celled organisms had developed on an infant
Earth,
these stones had coalesced in the hard vacuum of space, and there they
had
circled our young sun as small members of our planetary family.

So, how
did this chunk of space rock end up in my hand? At some point in the
evolution of our solar system, a number of large asteroid-type bodies
coexisted with our adolescent planets. Circling around the sun in a
chaotic dance of creation, these bodies would cross each other orbits
and eventually some of them collided. These collisions were violent and
they tore apart the parent bodies of the meteorites, smashing them to
bits. These tiny bits (meteoroids) of debris continued on in their own
orbits until a combination of fate and physics led them to cross paths
with Earth. They were captured by Earth's gravity and pulled down
through our atmosphere for a fiery descent. Many meteors will be burned
up completely in the violent passage through our dense atmosphere. But
some were large enough and hardy enough to survive the trip and they
landed on the ground intact.

Once a
meteoriod enters
the atmosphere, it becomes a meteor - that familiar shooting star
streak
of light that kids
make wishes on and adult stargazers delight in seeing. And once that
meteor
hits the ground, it becomes a meteorite. This rain of falling
meteorites
has continued, unabated, for billions (and billions) of years. The
deserts
and snowfields of the world are literally peppered with meteorites that
have
fallen over the two to three million years. Many oxidize away and are
never
found because the Earth is not a meteorite-friendly environment. In
space,
there is no oxygen, moisture, or wind, so the meteorites exist in a
nearly-perfect
state of "deep freeze" where they are protected from the effects
of weathering. Once the meteorites are exposed to Earth's air, wind and
water,
they begin to break down and terrestrialize. Stony-type meteorites with
simply
weather away into their base components and will eventually lose their
identity
as meteorites. Iron-type meteorites will likewise rot into a pile of
rusty
iron shale fragments. If the meteorites are not collected and
preserved,
they are simply lost forever.

Any
article that would attempt to explain all the various types of
meteorites, how they were formed, and what they are made up of, would
entail far more space than I have here. Indeed, entire libraries of
books have been written on the subject, and much is still unknown or
under debate about meteorites. Here I will attempt to briefly detail
the major types of meteorites and what makes them interesting to
science and the layman collector.

There
are 3 main types of meteorites - stony, iron, and stony-iron. Stony
meteorites are exactly what they sound like, they are rocky
combinations of minerals that could be easily mistaken for an Earth
rock if not for their peculiar properties.

(photo
above is a 3-pound unclassified stony meteorite from Morocco.)

Iron
meteorites are pieces of solid metal that are very dense and contain
high concentrations of the element nickel. Imagine something as dense
as a piece of a railroad track and you get some idea how heavy iron
meteorites are for their size.

(photo
above is an iron meteorite from the famous Canyon Diablo crater in
Arizona.)

Stony-irons
are a combination of the two types - part stone and part iron, mixed
together into a single mass.

(photo
above is a slice of Seymchan Pallasite, courtesy of the G. Gibbs
Collection.)

While
stony meteorites
are more common, iron meteorites are more resilient, tend to resist
weathering,
and
survive impact more often than some stony types.In addition to these 3
major
types of meteorites, there are many sub-types and variations which
would
fill up an encyclopedia (see Richard Nortonës ìEncyclopedia of
Meteoritesì for a complete treatment of all the types). Some of the
most interesting of the rare types are the so-called "planetary"
meteorites.
Planetary meteorites have been determined to originate from large
familiar
parent bodies, like the Moon and Mars. Yes, you heard correctly - some
meteorites
are actually fragments of our Moon and the planet Mars! How is it
possible
that a piece of the Moon or Mars ended up on Earth? In fact, most of
the
craters you can observe on the Moon were caused by meteorite impacts! A
large
meteorite that was a mile across (or bigger) slammed into the surface
of
the Moon or Mars. The resulting catastrophic impact and explosion
hurled
large amounts of material upwards which escaped the feeble gravity of
these
planets and escaped into space. These fragments then floated around in
the
solar system until they crossed paths with Earth's orbit and were
captured
by our gravity. In this manner, small pieces of other worlds can
actually
land on Earth! These planetary meteorites are the rarest of the rare
and
are highly desired by collectors and scientists alike for what they can
teach
us about the evolution of planets, including our own.

Now I
would like to address
the obvious question - how do we really know it's a meteorite? I get
that
question
all the time, mostly from people who are curious about meteorites, but
have
no prior experience with them. This is a relatively easy question to
answer
because meteorites possess some peculiar properties that are not
present
in Earthly materials. First and foremost is the content of elemental
nickel.
Pure nickel is exceedingly rare in the Earth's crust and the vast
majority
of the Earth's nickel is found in deep down in the core of our planet.
The
nickel that is present on the surface or the Earth (or near the
surface)
is contained in combined ores and not in a pure elemental form. Pure
nickel
must be extensively processed out from the raw ore, and one just
doesn't
find rocks or minerals with pure nickel in them. Any "rock" that has a
high nickel content is automatically a meteorite suspect. One can
easily determine a sample's nickel content by doing a simple chemical
reaction test. Another hallmark of meteorites is "chondrules" - which
are small spheres of various minerals which are embedded in the body
(or ìmatrixì)
of the meteorite. These chondrules are distinctive and unlike any
Earthly
formation of minerals. On a sliced meteorite, chondrules will appear as
little
circles embedded in the rocky matrix, this is the result of the saw
cutting
through the spherical chondrules - revealing them in cross section.
Chondrules
are the product of processes that are not present on Earth, so if one
has
a rock with chondrules in it,then it's a meteorite. There are other
litmus
tests as well, including specific gravity, and the degree of magnetic
attraction.

As
recently as the turn of the 20th century, the exact origin and nature
of meteorites was under hot debate, but after decades of scientific
study, meteorites are now well-understood and can be easily
distinguished from Earthly materials. But how do we know a Martian
meteorite is really from Mars or that a Lunar meteorite is really from
the Moon? The answer is again found in chemical and physical analysis.
Thanks to the astronauts of the Apollo program, we have actual Moon
rocks that were brought back from the surface of the Moon. Comparing
these known Moon rocks against suspected Lunar meteorites allows us to
determine not only that a meteorite came from the Moon, but we can also
determine if the meteorite came from the low-lying lunar basins or the
mountains of the lunar highlands - because each have their own chemical
and physical signatures. In the case of Martian meteorites, we can
compare their chemistries against the known chemistries of Martian
materials that we have analyzed with remote Martian rovers like
Sojourner. There is now no doubt that such meteorites are truly pieces

Now
that we have established
what meteorites are and how we determine their origins, let's examine
how
the
meteorite finds it way onto the open marketplace. Most of the
meteorites
on the collector market come from the deserts of North West Africa.
These
meteorites are called "NWA" meteorites and the bulk of them come from
the Sahara desert. Any rock laying out in the middle of the open desert
is automatically suspect - afterall, how did this rock get there?In
areas such as the Sahara, where native rock is either absent or highly
distinctive, a curious looking rock that is out of place must have
fallen there from the sky. In some cases, the meteorite is actually
seen to fall to Earth by eyewitnesses - these meteorites are called
"witnessed falls". Regardless of whether the meteorite was a witnessed
fall, or an unwitnessed find, someone stumbles across it, recognizes it
as unusual and picks it up. This is mostly done by Bedouin nomads and
other desert dwellers who are intimately familiar with the sand dunes
and know something special when they see it. They collect these stones
from the open desert and bring them back to marketplaces in Morocco or
large rock shows like the one in Tucson every year. In these
marketplaces, Western collectors and dealers comb through the offerings
and purchase promising specimens to bring back to the states or Europe.
Sometimes these meteorites are relatively-common types and they are
sold as unclassified NWA meteorites (UNWA) - this means they have been
identified as meteorites due to their properties, but they have not
been formally analyzed by a laboratory. If a particular meteorite seems
promising as a potentially rare type (like a Lunar or Martian), then a
piece of it is sent off to a respected laboratory for analysis. This
analysis is intensive and can takes months of study, which includes
thin-sectioning and study with scanning electron microscopes and other
instruments to determine it's exact chemical composition. Once
analyzed, the meteorite can be compared to other known meteorites and
then it is officially "classified". A classified meteorite is given a
name and/or number in the official catalogue of the Meteoritical
Society. Classified meteorites typically have names like "NWA 869"
(meaning this meteorite originated from North West Africa) or a
place-name like "Bassikounou" which
means that particular meteorite was found near Bassikounou Mauritania.
Meteorites
whose exact place of discovery or fall are known are given place names
such
as the nearest post office or permanent landmark. Meteorites whose
exact
point of discovery cannot be determined (because they were moved and
then
sold at a marketplace) are given catalogue numbers like NWA 869.
Generally
speaking, since meteorites which are seen to fall (witnessed falls) are
more
rare than found meteorites (finds), then witnessed falls are more
valuable
to the collector.

At some
point, the meteorite is offered for sale on the marketplace by the
owner, finder, or dealer. Of course, the internet is a great boon to
collectors and there is wide variety of meteorites available from
dealer websites, eBay, and collector groups. There are some frauds
(like most hobbies that involve things worth money) and there will
always be someone trying to pass off a fake or misrepresented
meteorite. Since meteorites are more rare than diamonds or gold, one
must be a savvy buyer to avoid possible scams. The best way to ensure
that a meteorite being offered for sale is the real thing, is to check
the credentials of the seller. Credentials to look for include
membership in the Meteoritical Society and the IMCA (International
Meteorite Collectors Association). The IMCA is group of collectors and
dealers who maintain of code of standards and ethics for selling or
trading meteorites. The Meteoritical Society is official governing body
of meteorite study and it is comprised of scientists, collectors and
dealers. It is the Meteoritical Society that publishes the official
classifications of all meteorites. Both of these organizations are
generally a safe bet to buy legitimate meteorites from members. If
purchasing from a marketplace like eBay, use a good measure of common
sense and examine the seller's feedback ratings. Prices for meteorites
on the open market can vary widely from dealer to dealer. Unlike gold
or diamonds which have a regulated market with going rates, the price
of meteorites is dictated solely by supply and demand. One dealer may
charge $20 for a given meteorite and another dealer may be selling an
identical meteorite for $100, so it pays to shop around and compare
prices. Assuming one has purchased a meteorite, then what does one do
with it?

(photo
above is a collection of specimens using display cubes, stands and
Riker boxes.)

Meteorites
are fascinating for what they can teach us about the solar system
because they are 4+ billion year old ambassadors of outer space. It's a
thrill to hold something older than the Earth that once circled our sun
out in open space. Meteorites can be displayed, stored, and shared like
any other valuable collectible. What's more, meteorites make great
outreach props for astronomy. Children absolutely love meteorites! Give
a child a meteorite to hold and tell him/her it's a piece of a shooting
star and watch his/her eyes light up with wonder and delight! And at
this point, I think I should warn our readers that collecting
meteorites is much like eating potato chips - you can't have just one.
It's a very addictive hobby that meshes well with astronomy, telescopes
and stargazing. After all, one can look at the planets through a
telescope, then actually hold a piece of one in hand.

Meteorites
should be cared for like any other rare collectible - they should be
handled with care with properly maintained. This means keeping them
away from moisture and sources of oxidation which might damage or
degrade the meteorite. After handling a meteorite, it should be wiped
clean with a dry cloth and stored in a dry area. A tupperware container
with a packet of dessicant to absorb moisture is an ideal way to store
meteorites. With proper care, a meteorite will last for many
generations to come.

So you
want to learn more
about meteorites and collecting them? I strongly recommend two books
and
one magazine
for those who want to do their homework on meteorites. The first is
"Rocks From Space" by O. Richard Norton. This is the definitive book in
the field of meteorites and it covers every fundamental aspect of
meteorites and collecting. It is very approachable to the layman and is
not laden with dense math and complex terminology. The second book is
"Cosmic Debris" by John G. Burke. "Cosmic Debris" is
a more serious work for the advanced enthusiast and it covers the
history
of meteoritics from it's very beginnings hundreds of years ago to the
latest
theories of the 20th century. Cosmic Debris also includes a fascinating
chapter
on the folklore of meteorites and it discusses how meteorites were
looked
at by primitive peoples and the legends that surrounded these strange
objects
that fell from Heaven. Unfortunately, Cosmic Debris is no longer in
print,
but used copies can be found from online book dealers. Last but not
least,
there is Meteorite Magazine, which is the only hobby periodical
dedicated
solely to meteorites and their study. It is a quarterly publication of
the
Arkansas Center for Space and Planetary Sciences and it is loaded with
informative
articles and beautiful eye-candy photos. The interested reader will
find
that meteorites are much like astronomy in general - the people who are
interested
in these fields are very friendly and approachable folks who love to
share
their knowledge about subject.